The overall purpose is to develop applications of stable isotopes (C13, N15, O18) as probes in biochemical systems with the application of appropriate techniqus (NMR, GC-MS). In order to accomplish this objective the synthesis of molecules containing these isotopes enriched at selected positions is undertaken, notably synthesis of peptides containing C13 and N15 enriched amino acids. Carbon-13 or nitrogen-15 NMR will be used to study the structure and function in solution of such peptides, and proteins derived from them, utilizing the special advantages that such enrichment provides. Metabolic studies will be undertaken to investigate the use of stable isotopes as safe probes in human systems when a GC-MS instrument is available.